Walk into most companies and the website is designed, reviewed, and approved on a large desktop monitor. Mobile gets a glance at the end, a quick check that nothing looks obviously broken, and then it ships. The desktop version is treated as the real site and the mobile version as a courtesy.
That's backwards for almost every local and service business, because the majority of their visitors, often including the ones most ready to act, are on a phone. The experience you treat as secondary is the one most of your customers actually have.
section 01the phone is the default, not the exception
A person looking for a service nearby is usually doing it on their phone, frequently in a moment of real intent: standing somewhere, mid-errand, deciding now. They're tapping with a thumb, on a smaller screen, possibly on a slower connection, with less patience than they'd have at a desk.
That context changes everything about whether your site works. A form that's fine with a mouse becomes a chore with a thumb. A layout that's elegant at full width becomes a scroll marathon on a phone. A page that loads acceptably on office wifi crawls on a phone in a parking lot. None of it shows up when you only ever look at the desktop version.
section 02what gets missed from the monitor
Designing on desktop and checking mobile last means the mobile experience is, at best, a compression of decisions made for a different screen. The tap targets are an afterthought. The load time is whatever it is. The most important button sits below a pile of content that made sense in a wide column and doesn't on a phone.
These aren't small cosmetic gaps. They're conversion losses concentrated on exactly the visitors most likely to buy, the ones who pulled out their phone because they were ready.
section 03design for the screen the decision happens on
The fix is an inversion: build and judge for the phone first, because that's where the decision actually happens, and let the desktop experience be the larger, more comfortable version, rather than the other way around. Test on a real device, on a real connection, with a real thumb.
The mobile experience stopped being a secondary view a long time ago. For most of your customers, it's the only view they'll ever have. Treat it like the main event, because for them, it is.